The present application is related to the U.S. Pat. No. 4,503,821 patented Mar. 12, 1985 and co-pending application of Matsumura et al, Ser. No. 752,732, filed July 8, 1985, both commonly assigned.
This invention relates generally to a method and apparatus for controlling an amount of fuel injected into engine cylinders respectively so that torque generated by respective cylinders is uniform throughout the cylinders.
The amount of fuel injected into a multi-cylinder internal combustion engine has been conventionally controlled uniformly throughout all the cylinders in both gasoline engines and diesel engines. According to known electronic fuel injecting systems for gasoline engines, the valve-opening duration of electromagnetic valves respectively provided to individual cylinders is controlled such that the valve opening duration is common to all the cylinders. According to known electronically controlled diesel engines, which have been recently put in a practical application stage, the position of an injection amount-controlling member, such as a control rack or a spill ring, is controlled where the controlling member is common to all the cylinders.
Although such a control effected uniformly throughout all the cylinders of an engine is simple, there arises a problem of variation or scattering in injecting fuel amount throughout the cylinders. Therefore, in using conventional apparatus, high manufacturing precision is required when manufacturing various parts, such as injection valves, injection conduits or the like which are used in the injection system in order to reduce such cylinder-to-cylinder variation. Such high manufacturing precision or accuracy necessarily increases the manufacturing cost. Furthermore, even though the precision of the parts used have been increased to its limit so that cylinder-to-cylinder variation is minimized, the amount of fuel actually injected into engine cylinders may suffer from variation or scatter throughout cylinders due to secular change or external disturbance, such as a variation in actuating timing of intake and/or exhaust valves or the like.
Such a variation in amount of fuel injected into cylinders of an engine results in irregular rotation of the engine crankshaft. Especially during idling such irregular rotation is uncomfortable and noisy. Generally speaking, the engine rotational speed during idling is set to a low value in view of suppression of fuel consumption. On the other hand, it is desired, especially for passenger automobiles, that engine rotation during idling be as smooth as possible in order to provide comfortable environment. Particularly, the above-mentioned irregular rotation during idling is desired to be reduced to achieve stable engine rotation.
A method of correcting the amount of fuel as a countermeasure for resolving the above problem is known (see SAE No. 820,207 for instance). In this method, engine speed is detected before and after fuel injection or combustion at predetermined engine crank angles in connection with respective cylinders to that the amount of fuel supplied to respective cylinders is controlled such that the difference in engine speed between two measurements performed before and after fuel injection, becomes uniform throughout all the cylinders during idling state. In detail, this method utilizes the fact that the difference in engine speed between two measurements performed before and after fuel injection has a close relationship with torque generated by an associated cylinder.
However, since the above-mentioned known method can renew correction values or amounts suitable for idling state only, the renewed correction value cannot be used for other engine operating states or modes. In detail, when the renewed correction amounts are used for engine operation other than idling, vibrations and/or irregular rotation are apt to be greater due to the unbalance or unevenness of generated torque throughout cylinders caused from undesirably corrected amounts of fuel to respective cylinders.